Osteoarthritis (OA) is chronic, debilitating condition for which there is no cure. There is strong evidence that interleukin-1 (IL-1) serves as an intra-articular mediator of cartilage loss, pain and inflammation in OA. Its natural inhibitor, the IL-1 receptor antagonist (IL-1Ra), holds promise as an effective treatment, but clinical application is hindered by difficulty achieving and maintaining effective concentrations intra-articularly. We have worked to develop technologies for delivering the cDNA for IL-1Ra to cells in the capsular tissues of joints, such that these tissues become endogenous sites of sustained, elevated IL-1Ra production. This gene-based approach removes the need for repeated application of the recombinant protein while providing the greatest concentration of the gene product specifically at the site of disease. Direct intra- articular injection of certain recombinant viral vectors can provide expression of therapeutic transgenes at levels sufficient to halt arthritis in small animal models. With the use of immunologically compatible vectors and cDNAs, exogenous transgenes can be expressed indefinitely in cells that populate the capsular tissues. Adeno-associated virus (AAV) offers many advantages that favor its use as a gene delivery vehicle for treatment of arthritis. The development of double-stranded (self-complementary [sc]) vectors and alternate capsid serotypes overcomes previous deficiencies such that AAV can be realistically considered as a candidate for human application in OA. The present study will test the hypothesis that scAAV- mediated delivery of the cDNA for IL-1Ra locally to joints with OA will provide sustained therapeutic benefit. Horses provide a unique system in which to study intra-articular gene transfer for joint disease. Their joints are proportional in size to human knees, and they are vulnerable to the onset of OA. In Specific Aims 1 and 2 we will work to determine the utility of scAAV as a gene delivery system to joints of human scale by performing pharmacokinetic studies in equine joints, characterizing biodistribution and transgenic expression patterns following delivery of the cDNA for the homologous equine IL-1Ra (eqIL-1Ra). Lessons learned from this part of the study will be used in Specific Aim 3 to evaluate the capacity of scAAV- mediated delivery of eqIL-1Ra to inhibit the pathologies of an osteochondral fragmentation model of OA in horses. By studying the efficacy of scAAV-IL-1Ra gene therapy in this manner- on an appropriate scale and in a relevant disease context- a clear representation of its therapeutic capacity will emerge. If successful these studies will provide the necessary pharmacokinetic, safety and efficacy data to support the implementation of human trials. PUBLIC HEALTH RELEVANCE: This study is designed to explore the usefulness of a local gene therapy for osteoarthritis. It involves the injection into the joint of recombinant viral vectors containing genes, whose products protect the cartilage from degeneration. To examine the usefulness of this procedure on a human scale, we will perform safety and efficacy studies in the forelimb joints of horses. These joints are proportional in size to human knees, and they naturally develop osteoarthritis. Information from these studies will be used to support clinical trials in humans.